Many small arms, including most automatic weapons, have moveable component parts that move or recoil in response to the gas pressure produced by the firing of the weapon. A spring is typically provided in order to cushion the moveable component as it approaches a fully recoiled position, and also to return the moveable component to a rest position in preparation for firing the next round of ammunition. Generally speaking, the spring must have a relatively high pretension, relative to its spring constant, against the moveable component.
After the moveable component has moved to the fully recoiled position, the spring subsequently returns the moveable component in the opposite direction back to the rest position. The spring must exert enough force on the moveable component to quickly return it back to the rest position. In the process, the moveable component comes into contact with a stop or support which helps to define the rest position. The moveable component typically runs into the stop with a great deal of force, and thus ideally the spring must be strong enough so that the moveable component does not continue to vibrate significantly when it contacts the stop.
In the event the moveable component is not biased against the stop with enough force, such as when the force of the spring is low relative to its spring constant, it is then possible that the moveable component will continue to oscillate and vibrate after coming into contact with the stop. In such a situation, the moveable component will experience a relatively significant time delay before it resumes the rest position. During this period of delay, the position of the moveable component relative to the rest of the weapon is undefined, which can cause functional disturbances such as weapon failure. Accordingly, damping mechanisms have been developed.
A good example of a prior art damping mechanism is the well known FN-Browning automatic shotgun which appeared on the market around the turn of the century. The FN-Browning has gained extraordinarily extensive use and has been employed by many hunters since its introduction. The barrel has its own recoil spring that is fully independent of the locking spring that triggers the reloading process and acts on the breech. This recoil spring is a coil spring arranged around the magazine tube, which is positioned beneath and parallel to the barrel. A sleeve mounted on the bottom of the barrel encloses the magazine tube and is biased by the recoil spring. A slotted brake ring is positioned between the magazine tube and recoil sleeve. The brake ring is pressed against the magazine tube by the force of the recoil spring, thus providing a braking action against the outer surface of the magazine tube. Continued vibration of the recoil spring is therefore strongly damped and no longer influences function of the weapon.
However, the damping effect is directly dependent on the force that the spring exerts on the barrel or sleeve. Therefore, the damping force is weakest precisely in the region of the rest position. Moreover, the FN-Browning brake is known to be very reliable, but only when the known shotgun is used under ordinary hunting conditions. A completely oil-free magazine tube already leads to load inhibitions because of the dry friction that results and thus the high braking effect. Use under conditions involving sand or mud exposure (rare in hunting weapons, common in military weapons) is inconceivable.
Another well known prior art damping mechanism involves the use of oil dampers. Oil dampers are similar to the shock absorbers used in vehicles and, like automotive shock absorbers, oil dampers are insensitive to soiling. In principle, it would be reasonable to use appropriately dimensioned oil dampers in a small firearm in which continued vibration of a weapon part is to be avoided. However, the weight, price and space requirements of such oil dampers are high. Moreover, such oil dampers require maintenance in order to ensure trouble-free operation. Finally, oil damped weapons are unsuitable for use as military weapons, which must be able to function flawlessly even after years of storage in an arsenal without major maintenance or reconditioning.
A final manner of achieving adequate damping is to use a cushion of exhaust gas in order to delay the striking of the moveable weapon part against the stop or support. Unfortunately, weapons so equipped are very susceptible to soiling, and typically experience a loss of firing accuracy. Thus, despite its advantages, such a mechanism is not well-suited for use in a sharpshooter's weapon or a weapon with similar requirements on firing precision.
The use of elastomer bodies in weapons has long been known. For example, the homemade shotguns that enjoy widespread use in the Philippines use rubber tension springs as striker springs. The PPSH 41 Russian submachine gun used an elastomer body on the end stop of the breech. Historically, such weapons have proven unsatisfactory due to the fact that the elastomer element gradually degrades with use and does not withstand aggressive weapon lubricant and cleaning agents over the long term.
Some chemically resistant elastomers have since been developed. However, the use of a pressure-loaded or pre-loaded elastomer body as recoil spring, instead of a steel compression spring, is not known, due in part to the fact that since previous applications of elastomers in small firearms have not been promising.
Elastomers have the inherent property of hysteresis, i.e., the energy expended for elastic deformation is not fully released on rebound. Instead, part of the kinetic energy is effectively consumed by being converted to heat energy, which manifests itself as heating of the elastomer body. Hysteresis is generally more pronounced under frequent pulse-like impact loads, such as the type of loads expected in a weapon. Significant energy consumption must therefore be reckoned with. Further, in principle an elastomer material is incompressible, just like a liquid, and thus the elastomer body requires space into which it will expand as the body yields under load. However, in the case of known elastomer buffers, the elastomer body is susceptible to destruction if deformed beyond its strength limits.
Accordingly, in addition to many other objects, features and advantages that will become readily apparent to those skilled in the art upon reading the following description, one of the objects of the present invention is to provide a simple, light, cost-effective, maintenance free and durable damped spring mechanism for a firearm, especially small firearms.